Complex Spatial Filtering with Binary Masks

TLDR

Holograms are traditionally created via interference experiments, and a Fourier hologram in the Fraunhofer plane functions as an optical matched filter. The study proposes using a computer‑guided plotter to draw holograms. The hologram is drawn by a plotter, minified and recorded on film as a binary transmittance pattern. Binary holograms produce image quality comparable to conventional holograms and function as effective optical matched filters for character recognition.

Abstract

Usually a hologram is produced by means of an interference experiment. Here, however, we let a computer- guided plotter draw the hologram. The plot, which has to be minified and recorded on film, contains no grey, only binary transmittance values. Our binary holograms yield reconstructed images of a quality equal to that of images obtained from usual holograms of comparable dimensions. When a Fourier hologram is inserted into the Fraunhofer plane of a coherent image forming system, it acts as a special type of a spatial filter, a so-called optical matched filter. Our binary matched filter is suitable for optical character recognition, the same as the usual optical matched filter introduced by Vander Lugt.